The present invention relates generally to integrated circuit packaging and, more particularly, to lead frame with a mold locking feature formed in the die pad.
Generally, one or more integrated circuits (ICs) or “dies” are packaged in a way that allows the circuits to be used in larger systems and to protect the dies from environmental damage. Often, a lead frame is used to provide electrical interconnection between IO pads of the die with IO pads of external systems, e.g., a printed circuit board (PCB). A lead frame thus includes metal leads (used to couple signals in and out of the integrated circuit package) and possibly other elements such as power bars and die paddles (also known as die pads and die flags). Prior to assembly, the lead frame may have support structures (e.g., a metal frame and tie bars) that keep the leads and die pad in place. During the assembly process, the support structures may be removed. As used herein, the term “lead frame” may be used to refer to the collection of elements before or after assembly, regardless of the presence or absence of the support structures.
Within the IC package are bond wires that electrically connect bond pads on the die to the metal leads of the lead frame. The die, die pad, bond wires, and a portion of the leads are embedded in a non-conductive, rigid, and impervious encapsulant to protect the die, bond wires and interconnections from environmental contaminants such as water. The leads have an exposed portion outside of the package that allows for electrical interconnections between the packaged chip and external circuitry on, for example, a PCB or the like. Typical encapsulants are plastics such as epoxy, and the lead frame is typically made of copper or a copper alloy. The bond wires are usually made of gold, aluminum, copper, or a copper alloy.
Power integrated circuits, such as voltage regulators or power amplifiers, have field-effect transistors (MOSFET) or bipolar transistors that operate to variably couple current to a load. As a consequence of conducting current, the transistors generate heat that warms the chip as a whole, whereby the integrated circuit can be damaged if the temperature of the chip gets too high. One technique for cooling the chip is to configure the encapsulant so that one side of the die pad is exposed while leaving the other side (the side having the chip attached thereto) embedded in the encapsulant. This allows the die pad to be attached to a heat sink that extracts heat from the chip and out of the package.
As the packaged chip heats up and cools over time (thermally cycles), such as when it is soldered to a PCB and during normal operation of the chip, the encapsulant and the die pad can separate from each other since the thermal coefficient of expansion (CTE) of the mold compound (plastic) is different from that of the die pad (metal). This might cause the packaged device to fail if contaminants, such as moisture, enter the package along the separations. Accordingly, it would be advantageous to have a package design that resists separation of the mold compound from the die pad.